Liquid discharge apparatus, head unit, and control method of liquid discharge apparatus

ABSTRACT

A liquid discharge apparatus includes: a piezoelectric element that is displaced according to a voltage of a drive signal; a cavity which is filled with a liquid and of which an inside volume is changed due to the displacement of the piezoelectric element; a nozzle that communicates with the cavity and is capable of discharging the liquid; a charge source that supplies a charge to the piezoelectric element; and a connection path selecting section that causes the piezoelectric element and the charge source to be electrically connected to each other by using a first signal path or a second signal path. The charge source includes: a first auxiliary power source that outputs two types or more of voltages; and a second auxiliary power source that outputs three types or more of voltages by using the two types or more of voltages output from the first auxiliary power source.

The entire disclosure of Japanese Patent Application No. 2014-005664,filed Jan. 16, 2014 is expressly incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to a liquid discharge apparatus, a headunit, and a control method of the liquid discharge apparatus.

2. Related Art

As an ink jet printer that discharges ink and prints an image or adocument, a printer that uses piezoelectric elements (for example, piezoelement) is known. The piezoelectric elements are provided respectivelycorresponding to a plurality of nozzles in a head unit (print head) andare respectively driven in accordance with drive signals and thereby apredetermined amount of ink (liquid) is discharged from the nozzles at apredetermined timing. The piezoelectric element is a capacitive loadlike a capacitor in terms of electric power. Therefore, a sufficientcurrent is needed to operate the piezoelectric element of the nozzle.

Therefore, in the related art, a configuration is known, in which anoriginal signal of the drive signal is amplified by using an amplifiercircuit and the amplified drive signal is supplied to the head unit suchthat the piezoelectric element is driven. Examples of the amplifiercircuit includes a system of performing current amplification of theoriginal signal by using a class AB amplifier or the like (linearamplification, see JPA-2009-190287) or a system of demodulating by usinga low pass filter after pulse width modulation, pulse densitymodulation, or the like of the original signal (class D amplification,see JP-A-2010-114711). In addition, a system of switching a voltage thatis applied to a piezoelectric element (voltage switching system, seeJP-A-2004-153411) is also proposed, in addition to a configuration inwhich the original signal is amplified by using the amplifier circuit.

However, the linear amplification results in high power consumption andpoor energy efficiency. The class D amplification is higher in energyefficiency compared to the linear amplification, but has a problem of anoccurrence of electromagnetic interference (EMI) by switching a highcurrent at a high frequency. In addition, in the simple voltageswitching system described above, power saving is achieved to someextent, but still has to be improved.

SUMMARY

An advantage of some aspects of the invention is to provide a liquiddischarge apparatus in which energy efficiency is high, an occurrence ofEMI is suppressed, and power consumption is improved, a head unit, and acontrol method of the liquid discharge apparatus.

In order to achieve the advantage described above, a liquid dischargeapparatus according to an aspect of the invention includes: apiezoelectric element that is displaced according to a voltage of adrive signal; a cavity which is filled with a liquid and of which aninside volume is expanded and contracted due to the displacement of thepiezoelectric element; a nozzle that communicates with the cavity and iscapable of discharging the liquid by the expansion and contraction ofthe inside volume of the cavity; a charge source that supplies a chargeto the piezoelectric element; a first signal path to which a firstvoltage is applied by the charge source; a second signal path to which asecond voltage that is higher than the first voltage is applied by thecharge source; and a connection path selecting section that causes thepiezoelectric element and the charge source to be electrically connectedto each other by using the first signal path or the second signal pathaccording to the voltage of a control signal that controls the voltageof the drive signal and a hold voltage of the piezoelectric element. Thecharge source includes: a first auxiliary power source that outputs twotypes or more of voltages; and a second auxiliary power source thatoutputs three types or more of voltages which is used to be applied tothe piezoelectric element by using the two types or more of voltagesoutput from the first auxiliary power source.

In the liquid discharge apparatus according to the aspect, theconnection path selecting section causes the piezoelectric element andthe charge source to be electrically connected to each other by usingthe first signal path or the second signal path, and thereby thepiezoelectric element is charged and discharged. Since the charge andthe discharge are performed in a stepwise manner, it is possible toachieve a high energy efficiency compared to a configuration in therelated art in which the charge or the discharge between power supplyvoltages is performed at once. In addition, in the charge source, sincethe second auxiliary power source outputs more voltages by using thevoltage output from the first auxiliary power source, it is possible toincrease the number of voltage divisions used when the drive signal issupplied to the piezoelectric element.

In the liquid discharge apparatus according to the aspect, the firstauxiliary power source may include: m (m is a plural number) capacitiveelements; and a first switching section that switches between a seriesstatus in which the m capacitive elements are electrically connected inseries and a parallel status in which the m capacitive elements areelectrically connected in parallel. The second auxiliary power sourcemay include: n (n is a plural number) capacitive elements; and a secondswitching section that switches between a series status in which the ncapacitive elements are electrically connected in series and a parallelstatus in which the n capacitive elements are electrically connected inparallel.

In this configuration, it is possible to match the intervals of the twotypes or more of voltages output from the first auxiliary power source.In addition, it is possible to match the intervals of the three types ormore of voltages output from the second auxiliary power source.

According to the configuration, in the second auxiliary power source inthe series status, any first point of connection points of the ncapacitive elements to one another may be connected to the first signalpath and a second point on the higher side than the first point of theconnection points of the n capacitive elements to one another may beconnected to the second signal path. Since the charge collected throughthe first signal path is distributed by the parallel connection of the mcapacitive elements and is supplied to and reused by the first signalpath and the second signal path by the series connection, it is possibleto suppress power consumption.

According to the configuration, the first auxiliary power source may beconfigured to supply, to the second auxiliary power source, at least oneof a higher-side voltage set in which a higher side has an A voltage anda lower-side voltage set in which the higher side has a B voltage thatis lower than the A voltage. The A voltage and the B voltage are justnominal labels to distinguish the voltages from each other.

According to the configuration, the first auxiliary power source may beconfigured to supply, to the second auxiliary power source, thehigher-side voltage set in a case where the voltage of the drive signalis a first drive voltage and the lower-side voltage set in a case wherethe voltage of the drive signal is a second drive voltage which is lowerthan the first drive voltage. In this configuration, the voltage setsthat the first auxiliary power source supplies to the second auxiliarypower source are switched according to the voltage of the drive signalthat is applied to the piezoelectric element. The voltage sets areswitched according to the voltage of the drive signal, which isperformed with a hysteresis characteristic.

According to the configuration, a third drive voltage which is lowerthan the first drive voltage and higher than the second drive voltagemay be included both in a voltage range of the higher-side voltage setand in a voltage range of the lower-side voltage set. In theconfiguration, since there is a range in which the voltage range of thehigher-side voltage set and the voltage range of the lower-side voltageset are overlapped, it is possible to suppress reduction of a followingproperty of the voltage of a signal (drive signal) which is applied tothe piezoelectric element, to a control voltage.

The invention can be realized in various aspects such as a controlmethod of the liquid discharge apparatus or a single head unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a diagram schematically illustrating a configuration of acontrol unit and a head unit of a printing apparatus.

FIG. 2 is a view illustrating a configuration of a discharge section inthe head unit.

FIG. 3 is a waveform diagram illustrating an example of a control signalCOM which is supplied to the head unit.

FIG. 4 is a block diagram illustrating a configuration of maincomponents of the printing apparatus.

FIG. 5 is a diagram illustrating an operation of an auxiliary powersupply circuit with respect to a voltage of a control signal Vin.

FIGS. 6A and 6B are diagrams illustrating connections in the auxiliarypower supply circuit.

FIG. 7 is a diagram illustrating an example of a configuration of adriver in the head unit.

FIG. 8 is a diagram illustrating an operational range of each levelshifter in the driver.

FIGS. 9A and 9B are diagrams illustrating examples of relationshipsbetween inputs and outputs in the driver.

FIGS. 10A, 10B, and 10C are diagrams illustrating examples ofrelationships between inputs and outputs in the level shifter.

FIG. 11 is a diagram illustrating flow of a current (charge) in thedriver.

FIG. 12 is a diagram illustrating flow of the current (charge) in thedriver.

FIG. 13 is a diagram illustrating flow of the current (charge) in thedriver.

FIG. 14 is a diagram illustrating flow of the current (charge) in thedriver.

FIG. 15 is a diagram illustrating an example of a configuration of afirst CP circuit in the auxiliary power supply circuit.

FIGS. 16A and 16B are diagrams illustrating operations of the first CPcircuit.

FIG. 17 is a diagram illustrating an example of a configuration of asecond CP circuit in the auxiliary power supply circuit.

FIGS. 18A and 18B are diagrams illustrating operations of the second CPcircuit.

FIG. 19 is a diagram illustrating loss during charging and dischargingof a piezoelectric element according to an embodiment.

FIG. 20 is a diagram illustrating loss during charging and dischargingof a piezoelectric element according to Comparative Example 1.

FIG. 21 is a diagram illustrating loss during charging and dischargingof a piezoelectric element according to Comparative Example 2.

FIG. 22 is a block diagram illustrating a configuration of maincomponents of a printing apparatus according to Application Example (1).

FIG. 23 is a diagram illustrating an operation or the like of anauxiliary power supply circuit according to Application Example (1).

FIGS. 24A and 24B are diagrams illustrating connections in the auxiliarypower supply circuit according to Application Example (1).

FIGS. 25C and 25D are diagrams illustrating connections in the auxiliarypower supply circuit according to Application Example (1).

FIG. 26 is a block diagram illustrating a configuration of maincomponents of a printing apparatus according to Application Example (2).

FIG. 27 is a diagram illustrating an operation or the like of theauxiliary power supply circuit according to Application Example (2).

FIGS. 28A and 28B are diagrams illustrating connections in the auxiliarypower supply circuit according to Application Example (2).

FIGS. 29C and 29D are diagrams illustrating connections in the auxiliarypower supply circuit according to Application Example (2).

FIG. 30E is a diagram illustrating connections in the auxiliary powersupply circuit according to Application Example (2).

FIG. 31 is a diagram illustrating an example of a configuration of asecond CP circuit according to Application Example (2).

FIGS. 32A and 32B are diagrams illustrating operations of the second CPcircuit.

FIG. 33 is a diagram illustrating an example of a configuration of adriver according to Application Example (3).

FIGS. 34A and 34B are diagrams illustrating operational ranges oftransistors according to Application Example (3).

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments according to the invention will be describedwith reference to the drawings.

Entire Configuration of Printing Apparatus

A printing apparatus according to the embodiment is an ink jet printer,that is, a liquid discharge apparatus, which discharges ink according toimage data supplied from a host computer such that an ink dot group isformed on a printing medium such as paper, and thereby prints an image(including a text, a figure, or the like) in accordance with the imagedata.

FIG. 1 is a diagram schematically illustrating a configuration of aprinting apparatus 1.

As illustrated in FIG. 1, the printing apparatus 1 is configured to havea control unit 10 that executes a computing process for printing animage on the basis of the image data supplied from the host computer anda head unit 20 that has a plurality of nozzles. The control unit 10 andthe head unit 20 are electrically connected through a flexible cable190. In addition, the head unit 20 is mounted on a carriage (notillustrated) which is movable in a direction (main scanning direction)substantially orthogonal to a feed direction (sub scanning direction) ofthe print medium.

The control unit 10 includes a main controller 120, digital to analogconverters (DAC) 160 and 164, and a main power supply circuit 180.

The main controller 120 executes a computing process for printing, suchas an image display process, color conversion process, ink colorseparating process, or a halftone process on the basis of the image dataacquired from the host computer and generates a plurality of types ofsignals for causing the ink to be discharged from a nozzle of the headunit 20. The plurality of types of signals include digital control datadCOM which is supplied from the DAC 160, or various signals to besupplied to a head controller 220 which will be described later.

Details of each computing process for printing which is executed by themain controller 120 may be executed by the host computer in some cases.The details of the computing process are so well known in the technicalfield of the printing apparatus that a description thereof is omitted.

In addition, as for the printing apparatus 1, a carriage motor to move acarriage mounted on the head unit in the main scanning direction, atransport motor for transporting the printing medium in the sub scanningdirection, and the like are included, and as for the control unit 10, aconfiguration of supplying drive signals to these motors are included,but similarly, these are so well known that a description thereof isomitted.

The DAC 160 converts the control data dCOM into an analog control signalCOM and supplies the converted signal to the head unit 20.

The main power supply circuit 180 supplies a power supply voltage toeach component of the control unit 10 or to the head unit 20 andparticularly supplies Vp and G as the power supply voltage to the headunit 20.

G (ground) is ground potential, and is a reference of a zero voltage, aslong as there is no specific description. In addition, the voltage Vp ison the higher side than the ground G according to the embodiment.

One or a plurality of color inks is supplied to the head unit 20 from anink container through a flow path, which is not illustratedspecifically. The head unit 20 includes a plurality of sets of drivers30 and piezoelectric elements (piezo element) 40, in addition to anauxiliary power supply circuit (charge source) 50, the head controller220, and the selection section 230.

The auxiliary power supply circuit 50 generates voltages V₀ to V₆ byusing the power supply voltages Vp and G by the main power supplycircuit 180 and supplies the voltages to the plurality of drivers 30, incommon. A configuration of the auxiliary power supply circuit 150 willbe described in detail, but each of the voltages V₀ to V₆ is notconstant normally according to the present embodiment and is configuredto be switched according to the voltage of the control signal COM.

The head controller 220 controls selection of the selection section 230in accordance with various signals supplied from the main controller120.

The selection sections 230 have switches 232 respectively correspondingto the plurality of sets of drivers 30 and piezoelectric elements 40.While one ends of the switches 232 are connected to one another and aresupplied with the control signal COM in common, the other ends areconnected to the corresponding input ends of the drivers 30. Each switch232 switches between ON/OFF in accordance with the control by the headcontroller 220 and supplies the control signal COM to the driver 30during the ON state, and cuts off the control signal COM during the OFFstate. Therefore, the selection section 230 selects the control signalCOM supplied from the control unit 10 in accordance with the headcontroller 220 and supplies the selected signal to the driver 30.

For the convenience of description, a control signal selected inaccordance with the head controller 220 and supplied to the driver 30among the control signals COM is described as Vin.

The driver 30 outputs a drive signal of a voltage Vout in accordancewith the control signal Vin which is supplied from the selection section230 by using the voltages V₀ to V₆ which are supplied from the auxiliarypower supply circuit 50 and drives the piezoelectric element 40.

One end of the piezoelectric element 40 is connected to an output end ofthe corresponding driver 30 and the other end of the piezoelectricelement 40 is connected in common to a ground G.

As described above, the piezoelectric element 40 is provided tocorrespond to each of the plurality of nozzles in the head unit 20 andcauses the ink to be discharged by the driving. Next, a configurationfor discharging the ink by driving the piezoelectric element 40 will bedescribed concisely.

FIG. 2 is a view schematically illustrating a configuration of adischarge section 400 corresponding to one nozzle in the head unit 20.

As illustrated in FIG. 2, the discharge section 400 includes thepiezoelectric element 40, a vibration plate 421, a cavity (pressurechamber) 431, a reservoir 441, and a nozzle 451. The vibration plate 421is deformed (flexurally vibrated) by the piezoelectric element 40provided on the top surface in FIG. 2 and causes an inside volume of thecavity 431 which is filled with the ink to expand/contract. The nozzle451 is provided in a nozzle plate 432 and is an opening through whichcommunication to the cavity 431 is performed.

The piezoelectric element 40 illustrated in FIG. 2 is called a unimorph(monomorph) type in general and has a configuration in which apiezoelectric body 401 is interposed between a pair of electrodes 411and 412. The central portion of the piezoelectric body 401 with theconfiguration is bent in the vertical direction with respect to both endportions in FIG. 2 according to the voltage applied between theelectrodes 411 and 412 along with the electrodes 411 and 412 and thevibration plate 421. Here, the upward bending causes the inside volumeof the cavity 431 to expand, and thus the ink is caused to be gatheredfrom the reservoir 441 and the downward bending causes the inside volumeof the cavity 431 to contract, and thus the ink is caused to bedischarged from the nozzle 451.

The piezoelectric element 40 is not limited to the unimorph type, butmay be a type such as a bimorph type or a stacked type, as long as thepiezoelectric element 40 is caused to deform such that a liquid such asink can be discharged. In addition, the piezoelectric element 40 is notlimited to a configuration of the flexural vibration, but may have aconfiguration of longitudinal vibration.

FIG. 3 is a diagram illustrating an example of a control signal COMwhich is supplied to the head unit 20.

As illustrated in FIG. 3, the control signal COM has a waveform which iscontinuous from a waveform (trapezoidal waveform) pattern PCOM1 that isthe minimum unit of the signal to drive the piezoelectric element 40 toa waveform pattern PCOM4 in time series in a printing cycle Ta. Thecontrol signal COM is practically a waveform which is repeated with theprinting cycle Ta as one cycle.

In the printing cycle Ta, the waveform pattern PCOM1 is positioned in afirst period T1, the waveform pattern PCOM2 is positioned in a secondperiod T2, the waveform pattern PCOM3 is positioned in a third periodT3, and the waveform pattern PCOM4 is positioned in a fourth period T4.

The waveform patterns PCOM1 to PCOM4 have a voltage Vc at the time ofeach start and at the time of each end.

The waveform patterns PCOM2 and PCOM3 according to the presentembodiment are substantially the same as each other. When it is assumedthat each of the waveforms is supplied to the piezoelectric element 40,the waveforms cause a predetermined amount, for example, substantially amedium amount of ink to be discharged from the nozzle.

To be more clear, the central portion of the piezoelectric element 40 isbent upward with respect to both the end portions in accordance with theincrease of the voltage, which causes the inside volume of the cavity431 to expand, such that the ink is gathered into the cavity 431,whereas the central portion of the piezoelectric element 40 is bentdownward with respect to both the end portions in accordance with thedrop of the voltage, which causes the inside volume of the cavity 431 tocontract, such that the ink is discharged from the nozzle 451.

In addition, the waveform pattern PCOM4 is a waveform different from thewaveform pattern PCOM2 (PCOM3). When it is assumed that the waveformpattern PCOM4 is supplied to the piezoelectric element 40, the waveformcause an amount of ink less than the predetermined amount to bedischarged from the nozzle.

The waveform pattern PCOM1 is a waveform for causing the ink in thevicinity of the opening of the nozzle to vibrate minutely and thuspreventing the viscosity of the ink from increasing. Therefore, eventhough the waveform pattern PCOM1 is supplied to the piezoelectricelement 40, no ink droplets are discharged from the nozzle.

Meanwhile, 2-bit print data that regulates an amount of ink (gradation)to be discharged from the nozzle for each pixel, a pulse that regulatesa start timing of the printing cycle Ta, a pulse that regulates starttimings of the periods T2, T3, and T4, or the like is supplied to thevarious signals that are supplied to the main controller 120.

The head controller 220 selects the control signal COM in accordancewith the various signals supplied from the main controller 120 for eachdriver 30 as follows and supplies the selected control signal COM as thecontrol signal Vin.

FIG. 3 illustrates how the control signal COM is selected with respectto the 2-bit print data by the head controller 220 and the selectionsection 230 and is supplied as the control signal Vin.

To be more specific, when the print data corresponding to a certainnozzle is, for example, (11), the head controller 220 causes the switch232 corresponding to the nozzle to be ON in the periods T2 and T3.Therefore, the waveform patterns PCOM2 and PCOM3 are selected out of thecontrol signals COM and become the control signal Vin. As will bedescribed later, the driver 30 outputs the drive signal of the voltageVout to follow the voltage of the control signal Vin and drives thepiezoelectric element 40 corresponding to the nozzle. Therefore, asubstantially medium amount of ink is discharged twice from the nozzlescorresponding to each other. Accordingly, the inks land and combine onthe printing medium, and as a result, a large dot is formed.

In addition, when the print data corresponding to a certain nozzle is(01), the head controller 220 causes the switch 232 corresponding to thenozzle to be ON in the periods T3 and T4. Therefore, since the waveformpatterns PCOM3 and PCOM4 are selected out of the control signals COM anddrive the piezoelectric element 40, substantially a medium and asubstantially small amount of ink is discharged twice from the nozzlecorresponding to each other. Accordingly, the inks are landed andcombined on the printing medium, and as a result, a medium dot isformed.

meanwhile, when the print data corresponding to a certain nozzle is(10), the head controller 220 causes the switch 232 corresponding to thenozzle to be ON in the period T4. Therefore, since the waveform patternPCOM4 is selected out of the control signals COM and drives thepiezoelectric element 40, substantially a small amount of ink isdischarged once from the nozzle. Accordingly, a small dot is formed.

when the print data corresponding to a certain nozzle is (00), the headcontroller 220 causes the switch 232 corresponding to the nozzle to beON in the period T1. Therefore, the waveform pattern PCOM1 is selectedout of the control signals COM and drives the piezoelectric element 40,but the ink in the vicinity of the opening of the nozzle in the periodT1 is caused to only minutely vibrate. Accordingly, since no ink isdischarged, no dot is formed on the printing medium, that is,non-recording occurs.

The control signal COM is selected according to such print data and issupplied as the control signal Vin (voltage Vout) and thereby fourgradations of the large dot, the medium dot, the small dot, and thenon-recording are expressed.

Such selection operations are executed concurrently for the nozzles.Further, waveforms illustrated in FIG. 3 are only examples. Practically,a combination of various waveforms prepared in advance is used accordingto the movement speed of a carriage, properties of the printing medium,or the like.

In addition, when the switch 232 switches to the OFF state, a feed pathfrom the output of the selection section 230 to the input of the driver30 is in a high impedance state. However, practically, the voltage Vc ismaintained by parasitic capacitance at the time of start and end of theperiods T1 to T4.

In addition, an example in which the piezoelectric element 40 is bentupward along with an increase of the voltage is described, but when thevoltage to be supplied to the electrodes 411 and 412 is inverted, thepiezoelectric element 40 is bent downward along with the increase of thevoltage. Therefore, in a configuration in which the piezoelectricelement 40 is bent downward along with the increase of the voltage, thecontrol signals COM illustrated in the drawings have waveforms invertedwith the voltage Vc as a reference.

As illustrated in FIG. 3, for example, in the period T1, the controlsignal Vin (voltage Vout) which is supplied to the piezoelectric element40 corresponding to a certain nozzle is either the waveform patternPCOM1 or the constant voltage Vc. In addition, in period T2, the controlsignal Vin (voltage Vout) which is supplied to the piezoelectric element40 corresponding to a certain nozzle is either the waveform patternPCOM2 or the constant voltage Vc.

That is, in each of the periods T1 to T4, the control signal Vin(voltage Vout) which is supplied to the piezoelectric element 40 iseither the control signal COM (waveform patterns PCOM1 to PCOM4) or theconstant voltage Vc.

FIG. 4 is a block diagram illustrating a configuration of maincomponents when focusing on a set of the driver 30 and the piezoelectricelement 40 in the printing apparatus 1.

The control signal Vin that is supplied to the driver 30 may be a signalwhich is obtained by extracting the control signal COM converted by theDAC 160 by the ON state of the switch 232 corresponding to the driver30, and then converting the extracted control signal COM into thevoltage Vc by the OFF state of the switch 232. Therefore, FIG. 4illustrates a configuration in which the control signal Vin is outputfrom a control signal generator 15 with the main controller 120 and theDAC 160 as a single block.

Meanwhile, according to the present embodiment, the auxiliary powersupply circuit (charge source) 50 includes a voltage comparator 505, afirst CP (charge pump) circuit 51, a second CP circuit 52, and aswitching device 535.

The first CP circuit 51, that is, a first auxiliary power source, causesthe power supply voltages Vp and G which are supplied from the mainpower supply circuit 180 to be divided and redistributed by using thecharge pump circuit such that voltages 4Vp/5, 3Vp/5, 2Vp/5, Vp/5 aregenerated.

The voltages are arranged in descending order as follows.

Vp>4Vp/5>3Vp/5>2Vp/5>Vp/5>G

However, according to the present embodiment, the voltage 4Vp/5 and thevoltage Vp/5 are not used, but the voltages 3Vp/5 and 2Vp/5 and thevoltage Vp and G are supplied to the switching device 535.

The switching device 535 is a two-pole two-throw switch according to thepresent embodiment, and thus selects either of a higher-side voltage set(Vp and 2Vp/5) or a lower-side voltage set (3Vp/5 and G) by aninstruction from the voltage comparator 505.

The voltage comparator 505 compares the voltage of the control signalCOM and a threshold value and issues an instruction of a voltage set tobe selected by the switching device 535 according to the comparedresult. Specifically, the voltage comparator 505 issues an instructionof selection of the higher-side voltage set (Vp and 2Vp/5) to theswitching device 535 when the voltage of the control signal COM is equalto or higher than the threshold value, and issues an instruction ofselection of the lower-side voltage set (3Vp/5 and G) when the voltageof the control signal COM is less than the threshold value.

However, the voltage comparator 505 has a hysteresis characteristic inthe comparison of the control signal COM. Specifically, the thresholdvalue includes a threshold value Vth-up which is used when the voltageof the control signal COM is increased and a threshold value Vth-dnwhich is used when dropped, and the threshold values Vth-up and Vth-dnare set to have a relationship of

(3Vp/5>)Vth-dn(>Vp/2)>Vth-dn(>2Vp/5)

For the convenience of the description, of the voltage sets that areselected in the switching device 535, a terminal at which thehigher-side voltage is output is written as Out-H and a terminal atwhich the lower-side voltage is output is written as Out-L.

In addition, since the higher-side voltage set and the lower-sidevoltage set are switched and output at the second CP circuit 52 by oneblock of the first CP circuit 51, the voltage comparator 505, and theswitching device 535, it is possible to consider the one block as thefirst CP circuit in a broad sense.

The second CP circuit 52, that is, the second auxiliary power sourcedivides the voltages that are output from output terminals Out-H andOut-L of the switching device 535 into six through dividing andredistribution by using the charge pump and outputs the dividedvoltages. To be more specific, when the voltage of the output terminalOut-H is written as V₆ and the voltage of the output terminal Out-L iswritten as V₀, a voltage (V₆-V₀) is divided into six and voltages V₄,V₄, V₃, V₂, and V₁ are output as intermediate voltages thereof indescending order.

As written in parentheses in FIG. 4, the driver 30 corresponds to aconnection path selecting section.

FIG. 5 is a diagram illustrating an operation of the auxiliary powersupply circuit 50 with respect to the voltage of the control signal COM.FIG. 5 illustrates a state in which the waveform pattern PCOM2 (orPCOM3) which has the greatest amplitude change is extracted among thecontrol signals COM for an illustration.

As illustrated in FIG. 5, a voltage range which the control signal COMcan have is equal to or higher than the voltage G (zero) and less thanthe voltage Vp.

As described above, when the voltage of the control signal COM becomesequal to or greater than the threshold value Vth-up in the course ofbeing increased, the voltage comparator 505 causes the switching device535 to switch to the voltage (Vp-2Vp/5) as the voltage (V₆-V₀). When thevoltage of the control signal COM becomes less than the threshold valueVth-up in the course of being dropped, the voltage comparator 505 causesthe switching device 535 to switch to the voltage (3Vp/5-G) as thevoltage (V₆-V₀). Therefore, the voltage (V₆-V₀) that is generated by thesecond CP circuit 52 is switched according to the voltage of the controlsignal COM as illustrated by (a) or (b) in the right column in FIG. 5.

In other words, in a case where the control signal Vin becomes thewaveform pattern of the control signal COM by the ON state of the switch232, switching is executed by the comparator 505 and the switchingdevice 535 such that the voltage of the control signal Vin is includedin a range of the voltage (V₆-V₀) which is supplied to the driver 30with respect to the change of the voltage of the control signal COM.

According to the present embodiment, the voltage Vc in the controlsignal COM is set in a range of being equal to or greater than thethreshold value Vth-up and less than the threshold value Vth-up.Therefore, even in a case where the control signal Vin has the voltageVc by the ON state of the switch 232 or at the time of start or end ofthe periods T1 to T4, the voltage Vc is included in the range of thevoltage (V₆-V₀) that is supplied to the driver 30 regardless of theswitching by the comparator 505 and the switching device 535.

In other words, the voltage Vc is positioned in an overlapping range ofthe voltage (Vp-2Vp/5) and the voltage (3Vp/5-G).

For the convenience of description, a section from a position where thevoltage of the control signal COM becomes equal to or greater than thethreshold value Vth-up in the course of being increased to a positionwhere the voltage of the control signal COM becomes less than thethreshold value Vth-dn in the course of being dropped is written as afirst section. In addition, a section from a position where the voltageof the control signal COM becomes less than the threshold value Vth-dnin the course of being dropped to a position where the voltage of thecontrol signal COM becomes equal to or greater than the threshold valueVth-up after the voltage of the control signal COM changes to beincreased is written as a second section.

FIGS. 6A and 6B are diagrams illustrating connections between the firstCP circuit 51 and the second CP circuit 52 in the auxiliary power supplycircuit 50. Since the first CP circuit 51 outputs the voltages Vp,3Vp/5, 2Vp/5, and G, the first CP circuit 51 is simply shown as fivecapacitive elements connected in series between the power supplyvoltages Vp and G in FIGS. 6A and 6B.

In the first section, the output terminal Out-H in the switching device535 has the voltage Vp and the output terminal Out-L has the voltage2Vp/5. Therefore, the first CP circuit 51 and the second CP circuit 52have a connection status as illustrated in FIG. 6A.

In addition, in the second section, the output terminal Out-H in theswitching device 535 has the voltage 3Vp/5 and the output terminal Out-Lhas the voltage G. Therefore, the first CP circuit 51 and the second CPcircuit 52 have a connection status as illustrated in FIG. 6B.

The piezoelectric element 40 is provided corresponding to each of theplurality of nozzles in the head unit 20 and is driven by the driver 30as a counterpart set to the piezoelectric element.

FIG. 7 is a diagram illustrating an example of a configuration of thedriver 30 that drives one piezoelectric element 40.

As illustrated in FIG. 7, the driver 30 includes an operationalamplifier 32, unit circuits 34 a to 34 f, and comparators 38 a to 38 e,and is configured to drive the piezoelectric element 40 in accordancewith the control signal Vin.

The driver 30 uses the voltage V₆ to V₀ and these seven types ofvoltages are supplied from the auxiliary power supply circuit 50 (secondCP circuit 52) through the wires 510 to 516, respectively.

The control signal Vin selected by the selection section 230 (switch232) is supplied to an input end (+) of the operational amplifier 32which is the input end of the driver 30.

An output signal of the operational amplifier 32 is supplied to each ofthe unit circuits 34 a to 34 f, returns to the input end (−) of theoperational amplifier 32 by negative feedback through resistance Rf, andis grounded to the ground G further through resistance Rin. Therefore,the operational amplifier 32 causes the control signal Vin to besubjected to (1+Rf/Rin) times of non-inverting amplification.

A voltage amplification rate of the operational amplifier 32 can be setby the resistances Rf and Rin, and for the sake of convenience,hereinafter, Rf is set to zero and Rin is set to be infinite. That is,hereinafter, it is described that the voltage amplification rate of theoperational amplifier 32 is set to “1”, and the control signal Vin issupplied as it is to the unit circuits 34 a to 34 f. It is needless tosay that the voltage amplification rate may be other than “1”.

The unit circuits 34 a to 34 f are provided in ascending order of thevoltages corresponding to two adjacent voltages to each other from seventypes of voltages V₆ to V₀. To be more specific,

the unit circuit 34 a corresponds to the voltage V₀ and the voltage V₁,the unit circuit 34 b corresponds to the voltage V₁ and the voltage V₂,the unit circuit 34 c corresponds to the voltage V₂ and the voltage V₃,the unit circuit 34 d corresponds to the voltage V₃ and the voltage V₄,the unit circuit 34 e corresponds to the voltage V₄ and the voltage V₅,andthe unit circuit 34 f corresponds to the voltage V₅ and the voltage V₆.

Circuit configurations of the unit circuits 34 a to 34 f are the same aseach other, and each includes one corresponding level shifter of thelevel shifters 36 a to 36 f, a bipolar NPN type transistor 341, and aPNP type transistor 342.

When the unit circuits 34 a to 34 f are described not specifically butgenerally, the unit circuit is described only with a reference number“34”. Similarly, level shifters 36 a to 36 f are described notspecifically but generally, the level shifter is described only with areference number “36”.

The level shifter 36 has either an enable status or a disable status. Tobe more specific, when an L-level signal is supplied to a negativecontrol end to which a circle is attached and an H-level signal issupplied to a positive control end to which no circle is attached, thelevel shifter 36 enters the enable status. Otherwise, the level shifter36 is in a disable status.

As will be described later, the comparators 38 a to 38 e are eachassociated with the intermediate five types of voltages V₁ to V₅ of theabove seven types of voltages, one to one.

Here, when a certain unit circuit 34 is focused on, an output signal ofthe comparator associated with a higher-side voltage of the two voltagescorresponding to the unit circuit 34 is supplied to the negative controlend of the level shifter 36 in the unit circuit 34. An output signal ofthe comparator associated with a lower-side voltage of the two voltagescorresponding to the unit circuit is supplied to the positive controlend of the level shifter 36.

However, while the negative control end of the level shifter 36 f in theunit circuit 34 f is connected to the wire 510 which supplies thevoltage V₀, the positive control end of the level shifter 36 a in theunit circuit 34 a is connected to the wire 516 which supplies thevoltage V₆.

In addition, in the enable status, the level shifter 36 shifts thevoltage of the input control signal Vin by a predetermined value in aminus direction and supplies the result to a base terminal of thetransistor 341, and simultaneously, the level shifter 36 shifts thevoltage of the control signal Vin by a predetermined value in a plusdirection and supplies the result to a base terminal of the transistor342. In the disable status, regardless of the control signal Vin, thelevel shifter 36 supplies a voltage that causes the transistor 341 to bein the OFF state, for example, the voltage V₆, to the base terminal ofthe transistor 341, and simultaneously, supplies a voltage that causesthe transistor 342 to be in the ON state, for example, the voltage V₀,to the base terminal of the transistor 342.

The predetermined value is set to a voltage (bias voltage, substantially0.6 volts) between the base-emitter which is measured when a currentstarts to flow to the emitter terminal. That is, the predetermined valueis a property determined according to the characteristics of thetransistors 341 and 342 and becomes zero if the transistors 341 and 342are in an ideal state.

A higher-side voltage of the corresponding two voltages is supplied to acollector terminal of the transistor 341, and a lower-side voltage issupplied to a collector terminal of the transistor 342.

For example, in the unit circuit 34 a corresponding to the voltage V₀and voltage V₁, the collector terminal of the transistor 341 isconnected to the wire 511 which supplies the voltage V₁ and thecollector terminal of the transistor 342 is connected to the wire 510which supplies the voltage V₀. In addition, in the unit circuit 34 bcorresponding to the voltage V₁ and voltage V₂, the collector terminalof the transistor 341 is connected to the wire 512 which supplies thevoltage V₂ and the collector terminal of the transistor 342 is connectedto the wire 511 which supplies the voltage V₁. In the unit circuit 34 fcorresponding to the voltage V₅ and voltage V₆, the collector terminalof the transistor 341 is connected to the wire 516 which supplies thevoltage V₆ and the collector terminal of the transistor 342 is connectedto the wire 515 which supplies the voltage V₅.

Meanwhile, emitter terminals of the transistors 341 and 342 in the unitcircuits 34 a to 34 f are connected commonly to an end of thepiezoelectric element 40 and a common connection point of the emitterterminals of the transistors 341 and 342 is connected to an end of thepiezoelectric element 40 as an output end of the driver 30.

A voltage of one end of the piezoelectric element 40 is described asVout.

The comparators 38 a to 38 e corresponding to five types of voltages V₁to V₅, respectively, compare the high and low of the voltages suppliedto two input ends and output a signal indicating the compared result.Here, the corresponding voltage is supplied to one end of the two inputends in the comparators 38 a to 38 e and the other end is connectedcommonly to the emitter terminals of the transistors 341 and 342 and oneend of the piezoelectric element 40. For example, in the comparator 38 acorresponding to the voltage V₁, the corresponding voltage V₁ issupplied to one end of the two input ends and in the comparator 38 bcorresponding to the voltage V₂, the corresponding voltage V₂ issupplied to one end of the two input ends.

Each of the comparators 38 a to 38 e outputs an H-level signal when thevoltage Vout at one end of the input end is equal to or higher than thevoltage of the other end, and outputs an L-level signal when the voltageVout is less than the voltage of the other end.

Specifically, the comparator 38 a outputs an H-level signal when thevoltage Vout is equal to or higher than the voltage V₁, and outputs anL-level signal when the voltage Vout is less than the voltage V₁. Inaddition, the comparator 38 b outputs an H-level signal when the voltageVout is equal to or higher than the voltage V₂, and outputs an L-levelsignal when the voltage Vout is less than the voltage V₂.

When one voltage is focused on out of the five types of voltages, theconfiguration is the same as above in that the output signal from thecomparator corresponding to the focused-on voltage is supplied to bothof a negative input end of the level shifter 36 of the unit circuit inwhich the voltage becomes the higher-side voltage and a positive inputend of the level shifter 36 of the unit circuit in which the voltagebecomes the lower-side voltage.

For example, the output signal from the comparator 38 a corresponding tothe voltage V₁ is supplied to both of a negative input end of the levelshifter 36 a of the unit circuit 34 a with which the voltage V₁ isassociated as the higher-side voltage and a positive input end of thelevel shifter 36 b of the unit circuit 34 b with which the voltage V₁ isassociated as the lower-side voltage. In addition, the output signalfrom the comparator 38 b corresponding to the voltage V₂ is supplied toboth of a negative input end of the level shifter 36 b of the unitcircuit 34 b with which the voltage V₂ is associated as the higher-sidevoltage and a positive input end of the level shifter 36 c of the unitcircuit 34 c with which the voltage V₂ is associated as the lower-sidevoltage.

When the voltages V₁, V₂, . . . represent a first voltage, a secondvoltage, . . . , respectively, the wires 511 and 512 . . . correspond toa first signal path, a second signal path, . . . , respectively.

Next, the operation of the driver 30 will be described.

The voltage (V₆-V₀) which is supplied to the driver is switched to thehigher-side voltage set or to the lower-side voltage set according tothe control signal COM. Here, a case of the higher-side voltage set isfirst described and then an operation in a case where switching to thelower-side voltage set occurs will be described later.

First, a description of checking the statuses of the level shifters 36 ato 36 f with respect to the voltage Vout at one end of the piezoelectricelement 40 is provided. In a case where the higher-side voltage set (Vpand 2Vp/5) is selected, the voltages V₆ to V₀ have a relationshipillustrated by (a) in the right column in FIG. 5.

FIG. 8 is a diagram illustrating a range of a voltage in which the levelshifters 36 a to 36 f are in the enable status with respect to thevoltage Vout.

First, in a first status in which the voltage Vout is less than thevoltage V₁, the output signals from the comparators 38 a to 38 e allhave the L level. Therefore, in the first status, only the level shifter36 a is in the enable status and the other level shifters 36 b to 36 fare in the disable status.

In a second status in which the voltage Vout is equal to or higher thanthe voltage V₁ and less than the voltage V₂, only the output signal fromthe comparator 38 b becomes the H level and the output signals from theother comparators become the L level. Accordingly, in the second status,only the level shifter 36 b is in the enable status and the other levelshifters 36 a and 36 c to 36 f are in the disable status.

Next, in a third status in which the voltage Vout is equal to or higherthan the voltage V₂ and less than the voltage V₃, only the level shifter36 c is in the enable status. In a fourth status in which the voltageVout is equal to or higher than the voltage V₃ and less than the voltageV₄, only the level shifter 36 d is in the enable status. In a fifthstatus in which the voltage Vout is equal to or higher than the voltageV₄ and less than the voltage V₅, only the level shifter 36 e is in theenable status. In a sixth status in which the voltage Vout is equal toor higher than the voltage V₅, only the level shifter 36 f is in theenable status.

When the level shifter 36 a is in the enable status in the first status,the level shifter 36 a supplies a voltage signal on which the levelshifting of the control signal Vin by a predetermined value is performedin the minus direction to the base terminal of the transistor 341 in theunit circuit 34 a, and supplies a voltage signal on which the levelshifting of the control signal Vin by the predetermined value isperformed in the plus direction to the base terminal of the transistor342 in the unit circuit 34 a.

Here, when the voltage of the control signal Vin is higher than thevoltage Vout (voltage of the connection point of the emitter terminalsto each other), a current in accordance with the difference (voltagebetween the base-emitter, to be more exact, voltage obtained bysubtracting a predetermined value from the voltage between thebase-emitter) flows from the collector terminal of the transistor 341 tothe emitter terminal thereof. Therefore, when the voltage Vout isgradually increased and approaches the voltage of the control signal Vinand eventually the voltage Vout reaches the voltage of the controlsignal Vin, the current flowing to the transistor 341 becomes zero atthis time.

Meanwhile, when the voltage of the control signal Vin is lower than thevoltage Vout, a current in accordance with the difference flows from theemitter terminal of the transistor 342 to the collector terminalthereof. Therefore, when the voltage Vout is gradually lowered andapproaches the voltage of the control signal Vin and eventually thevoltage Vout reaches the voltage of the control signal Vin, the currentflowing to the transistor 342 becomes zero at this time.

Accordingly, in the first status, the transistors 341 and 342 of theunit circuit 34 a execute control of the voltage Vout to reach thecontrol signal Vin.

Since, in the first status, the level shifter 36 is in the disablestatus in the unit circuits 34 b to 34 f except for the unit circuit 34a, the voltage V₆ is supplied to the base terminal of the transistor 341and the voltage V₀ is supplied to the base terminal of the transistor342. Therefore, since, in the first status, the transistors 341 and 342are in the OFF state in the unit circuits 34 b to 34 f, the transistors341 and 342 are not involved in the control of the voltage Vout.

Here, the operation in the first status is described, and the operationsin the second to sixth statuses are the same. To be more specific, anyone of the unit circuits 34 a to 34 f is activated according to thevoltage Vout held in the piezoelectric element 40, and the activatedtransistors 341 and 342 of the unit circuit 34 control the voltage Voutto reach the control signal Vin. Therefore, regarding all of the drivers30, the voltage Vout is caused to follow the voltage of the controlsignal Vin.

Accordingly, as illustrated in FIG. 9A, when the control signal Vin isincreased, for example, from the voltage V₀ to voltage V₆, the voltageVout follows the control signal Vin and also changes from the voltage V₀to voltage V₆. In addition, as illustrated in FIG. 9B, when the controlsignal Vin is lowered from the voltage V₆, the voltage Vout follows thecontrol signal Vin and also changes from the voltage V₆.

According to the present embodiment, when the control signal COM becomesequal to or greater than the threshold value Vth-up, the voltages V₆ toV₀ are switched to the higher-side voltage set, and when the controlsignal COM is less than the threshold value Vth-dn, the voltages V₆ toV₀ are switched to the lower-side voltage set.

FIGS. 10A to 10C are diagrams illustrating the operation of the levelshifter.

When the control signal Vin changes to be increased from the voltage V₀to voltage V₆, the voltage Vout is increased to follow the controlsignal Vin. In this increasing process, in the first status in which thevoltage Vout is less than the voltage V₁, the level shifter 36 a entersthe enable status. Therefore, as illustrated in FIG. 10A, the voltage(written as “P type”) which is supplied to the base terminal of thetransistor 341 by the level shifter 36 a becomes the voltage on whichthe shifting of the control signal Vin by the predetermined value isperformed in the minus direction, and the voltage (written as “N type”)which is supplied to the base terminal of the transistor 342 becomes thevoltage on which the shifting of the control signal Vin by thepredetermined value is performed in the plus direction. Meanwhile, inthe statuses other than the first status, since the level shifter 36 ais in the disable status, the voltage that is supplied to the baseterminal of the transistor 341 becomes V₆ and the voltage that issupplied to the base terminal of the transistor 342 becomes V₀.

FIG. 10B illustrates a voltage waveform output from the level shifter 36b and FIG. 10C illustrates a voltage waveform output from the levelshifter 36 f. As long as heed is paid to the process in which the levelshifter 36 b enters the enable status in the second status in which thevoltage Vout is equal to or higher than the voltage V₁ and less than thevoltage V₂, and the level shifter 36 f enters the enable status in thesixth status in which the voltage Vout is equal to or higher than thevoltage V₅ and less than the voltage V₆, a specific description is notnecessary.

In addition, a description of the operations of the level shifters 36 ato 36 f in the process of increasing the voltage (or voltage Vout) ofthe control signal Vin or a description of the operations of the levelshifters 36 a to 36 f in the process of lowering the voltage (or voltageVout) of the control signal Vin is omitted.

Next, flow of the current (charge) in the unit circuits 34 a to 34 fwill be described by taking examples of the unit circuits 34 a and 34 bboth during charging and during discharging.

FIG. 11 is a diagram illustrating the operation of the piezoelectricelement 40 which is charged in the first status (status in which thevoltage Vout is less than voltage V₁).

Since, in the first status, the level shifter 36 a is in the enablestatus and the other level shifters 36 b to 36 f are in the disablestatus, only the unit circuit 34 a may be focused on.

When the voltage of the control signal Vin is higher than the voltageVout in the first status, the transistor 341 of the unit circuit 34 acauses the current to flow in accordance with the voltage between thebase-emitter. Meanwhile, the transistor 342 of the unit circuit 34 a isin the OFF state.

During the charging in the first status, the current flows through apath from the wire 511 through the transistor 341 (of the unit circuit34 a) to the piezoelectric element 40 as illustrated by an arrow in FIG.11 such that the piezoelectric element 40 is charged with the charge.The voltage Vout is increased by the charging. Eventually, when thevoltage Vout approaches and reaches the voltage of the control signalVin, the transistor 341 of the unit circuit 34 a enters the OFF stateand thus the charging of the piezoelectric element 40 is stopped.

Meanwhile, in a case where the control signal Vin is increased to beequal to or higher than the voltage V₁, the voltage Vout follows thecontrol signal Vin and becomes equal to or higher than the voltage V₁.Therefore, the status is changed from the first status to the secondstatus (status in which the voltage Vout is equal to or higher than thevoltage V₁ and less than the voltage V₂).

FIG. 12 is a diagram illustrating the operation of the piezoelectricelement 40 which is charged in the second status.

In the second status, since the level shifter 36 b is in the enablestatus and the other level shifters 36 a and 36 c to 36 f are in thedisable status, only the unit circuit 34 b may be focused on.

When the voltage of the control signal Vin is higher than the voltageVout in the second status, the transistor 341 of the unit circuit 34 bcauses the current to flow in accordance with the voltage between thebase-emitter. Meanwhile, the transistor 342 of the unit circuit 34 b isin the OFF state.

During the charging in the second status, the current flows through apath from the wire 512 through the transistor 341 (of the unit circuit34 b) to the piezoelectric element 40 as illustrated by an arrow in FIG.12 such that the piezoelectric element 40 is charged with the charge.That is, in a case where the piezoelectric element 40 is charged in thesecond status, one end of the piezoelectric element 40 is connectedelectrically to the auxiliary power supply circuit 50 through the wire512.

When the status is changed from the first status to the second statusduring the increase of the voltage Vout, a current supplying sourceswitches from the wire 511 to the wire 512.

Eventually, when the voltage Vout approaches and reaches the voltage ofthe control signal Vin, the transistor 341 of the unit circuit 34 benters the OFF state and thus the charging of the piezoelectric element40 is stopped.

Meanwhile, in a case where the control signal Vin is increased to beequal to or higher than the voltage V₂, the voltage Vout follows thecontrol signal Vin and becomes equal to or higher than the voltage V₂.As a result, the status is changed from the second status to the thirdstatus (status in which the voltage Vout is equal to or higher than thevoltage V₂ and less than the voltage V₃).

Since the charging operations from the third status to the sixth statusare substantially the same, the current (charge) supplying sourcesswitch to wires 513, 514, 515, and 516 sequentially (not particularlyillustrated).

FIG. 13 is a diagram illustrating the operation of the piezoelectricelement 40 which is discharged in the second status.

In the second status, the level shifter 36 b is in the enable status.When the voltage of the control signal Vin is lower than the voltageVout in this status, the transistor 342 of the unit circuit 34 b causesthe current to flow in accordance with the voltage between thebase-emitter. Meanwhile, the transistor 341 of the unit circuit 34 b isin the OFF state.

During the discharging in the second status, the current flows through apath from the piezoelectric element 40 through the transistor 342 (ofthe unit circuit 34 b) to the wire 511 as illustrated by an arrow inFIG. 13 such that the charge is discharged from the piezoelectricelement 40. That is, in a case where the charge is charged in thepiezoelectric element 40 in the first status, and in a case where thecharge is discharged from the piezoelectric element 40 in the secondstatus, one end of the piezoelectric element 40 is connectedelectrically to the auxiliary power supply circuit 50 through the wire511. In addition, the wire 511 supplies the current (charge) during thecharging in the first status and collects the current (charge) duringthe discharging in the second status. The collected charge isredistributed and reused by the auxiliary power supply circuit 50.

Eventually, when the voltage Vout approaches and reaches the voltage ofthe control signal Vin, the transistor 342 of the unit circuit 34 benters the OFF state and thus the discharging of the piezoelectricelement 40 is stopped.

Meanwhile, in a case where the control signal Vin is lowered to be lessthan the voltage V₁, the voltage Vout follows the control signal Vin andbecomes less than the voltage V₁. As a result, the status is changedfrom the second status to the first status.

FIG. 14 is a diagram illustrating the operation of the piezoelectricelement 40 which is discharged in the first status.

In the first status, the level shifter 36 a is in the enable status.When the voltage of the control signal Vin is lower than the voltageVout in this status, the transistor 342 of the unit circuit 34 a causesthe current to flow in accordance with the voltage between thebase-emitter.

At this time the transistor 341 of the unit circuit 34 a is in the OFFstate.

During the discharging in the first status, the current flows through apath from the piezoelectric element 40 through the transistor 342 (ofthe unit circuit 34 a) to the wire 510 as illustrated by an arrow inFIG. 14 such that the charge is discharged from the piezoelectricelement 40.

Here, the unit circuits 34 a and 34 b are described as examples bothduring the charging and during the discharging. The unit circuits 34 cto 34 f operate in substantially the same way except that thetransistors 341 and 342 which control the current are different.

In addition, in the discharge path and the charge path in each status,the path from one end of the piezoelectric element 40 to the connectionpoint of the emitter terminals to each other in the transistors 341 and342 is shared.

According to the present embodiment, when the control signal COM is lessthan the threshold value Vth-dn, the voltages V₆ to V₀ are switched tothe lower-side voltage set illustrated by (b) on the right column inFIG. 5. Therefore, the voltage V₆ becomes the voltage 3Vp/5, the voltageV₀ becomes the voltage G, and the voltages V₅ to V₁ become theintermediate voltages which divide the voltage 3Vp/5 to voltage G intosix.

In the voltages V₆ to V₀ corresponding to the higher-side voltage setillustrated by (a) in the right column in FIG. 5, the threshold valueVth-dn is included in a range from the voltage V₁ to voltage V₀.Therefore, the level shifter 36 a enters the enable status in the driver30 immediately before the voltage of the control signal COM becomes lessthan the threshold value Vth-dn. Meanwhile, in the voltages V₆ to V₀corresponding to the lower-side voltage set illustrated by (b) in theright column in FIG. 5, the threshold value Vth-dn is included in arange from the voltage V₅ to voltage V₄. Therefore, the level shifter 36e enters the enable status in the driver 30 immediately after thevoltage of the control signal COM becomes less than the threshold valueVth-dn.

Accordingly, when the voltages are switched from the higher-side voltageset to the lower-side voltage set, the switching to the enable status isperformed from the level shifter 36 a to level shifter 36 e in thedriver 30. Therefore, the circuit to control the voltage Vout is changedfrom the unit circuit 34 a to the unit circuit 34 e. The subsequentoperations are the same as the case where the voltages V₆ to V₀ becomethe higher-side voltage set.

In addition, when the control signal COM is equal to or higher than thethreshold value Vth-up, the voltages V₆ to V₀ are switched from thelower-side voltage set illustrated by (b) to the higher-side voltage setillustrated by (a). Therefore, the voltage V₆ becomes the voltage Vp,the voltage V₀ becomes the voltage 2Vp/5, and the voltages V₅ to V₁become the intermediate voltages which divide the voltage Vp to voltage2Vp/5 into six.

In the voltages V₆ to V₀ corresponding to the lower-side voltage setillustrated by (b), the threshold value Vth-up is included in a rangefrom the voltage V₅ to voltage V₆. Therefore, the level shifter 36 fenters the enable status in the driver 30 immediately before the voltageof the control signal COM becomes equal to or higher than the thresholdvalue Vth-up. Meanwhile, in the voltages V₆ to V₀ corresponding to thehigher-side voltage set illustrated by (a), the threshold value Vth-upis included in a range from the voltage V₁ to voltage V₂. Therefore, thelevel shifter 36 b enters the enable status in the driver 30 immediatelyafter the voltage of the control signal COM becomes equal to or higherthan the threshold value Vth-up.

Accordingly, when the voltages are switched from the lower-side voltageset to the higher-side voltage set, the switching to the enable statusis performed from the level shifter 36 f to level shifter 36 b in thedriver 30. Therefore, the circuit to control the voltage Vout is changedfrom the unit circuit 34 f to the unit circuit 34 b. The subsequentoperations are as described above.

When the switch 232 is in the OFF state and the control signal Vin isthe voltage Vc, the voltage Vc is included in the range of the voltagesV₆ to V₀ regardless of the voltages V₆ to V₀ being the lower-sidevoltage set or the higher-side voltage set. Therefore, in the driver 30,control of the voltage Vout to become the voltage Vc of the controlsignal Vin is executed.

According to the present embodiment, when the voltages V₆ to V₀ areswitched to either the lower-side voltage set or the higher-side voltageset according to the voltage of the control signal COM and supplied tothe driver 30, the driver 30 controls the voltage Vout to become thevoltage of the control signal Vin that extracts the control signal COM(or replaced with the voltage Vc)

Next, the first CP circuit 51 and the second CP circuit 52 in theauxiliary power supply circuit 50 will be described.

FIG. 15 is a diagram illustrating an example of a configuration of thefirst CP circuit 51.

As illustrated in FIG. 15, the first CP circuit 51 is configured to haveswitches Sw3 d, Sw3 u, Sw4 d, Sw4 u, Sw5 d, Sw5 u, Sw6 d, and Sw6 u, andcapacitive elements C51, C52, C53, C54, C55, C1 a, C2 a, C3 a, and C4 a.

Among these components, the switches are all one-pole two-throw (singlepole double throw) switches and a common terminal is connected to anyone of terminals a and b in accordance with a control signal A/B. In abrief description, the control signal A/B is a pulse signal in which aduty ratio is substantially 50%, for example, and the frequency thereofis set to be about 20 times the frequency of the control signals COM.Such a control signal A/B may be generated by an internal oscillator(not illustrated) in the auxiliary power supply circuit 50 or may besupplied from the control unit 10 through the flexible cable 190. Thecapacitive elements C51, C1 a, C2 a, C3 a, and C4 a are used for chargetransfer. The capacitive elements C51, C52, C53, C54, and C55 are usedfor backup. Therefore, the capacitive element C51 serves as the elementfor both the charge transfer and the backup.

Practically, the above switches are configured by combining thetransistors in a semiconductor integrated circuit, and the capacitiveelements are mounted on the semiconductor integrated circuit externally.It is desired that the semiconductor integrated circuit have aconfiguration in which the plurality of drivers 30 described above isalso formed.

In the first CP circuit 51, the voltage Vp is supplied to one end of thecapacitive element C55 and to a terminal a of the switch Sw6 u. A commonterminal of the switch Sw6 u is connected to one end of the capacitiveelement C4 a and the other end of the capacitive element C4 a isconnected to a common terminal of the switch Sw6 d. A terminal a of theswitch Sw6 d is connected to one end of the capacitive element C54 andto a terminal a of the switch Sw5 u. A common terminal of the switch Sw5u is connected to one end of the capacitive element C3 a and the otherend of the capacitive element C3 a is connected to a common terminal ofthe switch Sw5 d. A terminal a of the switch Sw5 d is connected to oneend of the capacitive element C53 and to a terminal a of the switch Sw4u. A common terminal of the switch Sw4 u is connected to one end of thecapacitive element C2 a and the other end of the capacitive element C2 ais connected to a common terminal of the switch Sw4 d. A terminal a ofthe switch Sw4 d is connected to one end of the capacitive element C52and to a terminal a of the switch Sw3 u. A common terminal of the switchSw3 u is connected to one end of the capacitive element C1 a and theother end of the capacitive element C1 a is connected to a commonterminal of the switch Sw3 d. A terminal a of the switch Sw3 d isconnected to one end of the capacitive element C51 and to each terminalb of the switches Sw6 u, Sw5 u, Sw4 u, and Sw3 u. The other ends of thecapacitive elements C55, C54, C53, C52, and C51 and the terminals b ofthe switches Sw6 d, Sw5 d, Sw4 d, and Sw3 d, are commonly grounded tothe voltage G.

For example, when the switches Sw6 u and Sw6 d and the capacitiveelements connection pieces 55 and C4 a are considered as one stage, thefirst CP circuit 51 can have a configuration of a four-stage pluscapacitive element C51.

FIGS. 16A and 16B are diagrams illustrating the connection status of theswitches in the first CP circuit 51.

Each switch has two statuses of a status (status A) in which the commonterminal is connected to the terminal a by the control signal A/B and astatus (status B) in which the common terminal is connected to theterminal b. FIG. 16A illustrates the connection of the status A in thefirst CP circuit 51 and FIG. 16B illustrates the connection of thestatus B by using equivalent circuits in a simplified manner,respectively.

In the status A, the capacitive elements C4 a, C3 a, C2 a, C1 a, and C51are connected in series between the voltages Vp and G. Therefore, thestatus A may be called a series status. Meanwhile, in the status B,one-side ends of the capacitive elements C4 a, C3 a, C2 a, C1 a, and C51are commonly connected to one another. Therefore, the status B may becalled a parallel status. In the status B, since the capacitive elementsC4 a, C3 a, C2 a, C1 a, and C51 are connected in parallel to oneanother, the hold voltage is equalized.

The switches Sw3 d, Sw3 u, Sw4 d, Sw4 u, Sw5 d, Sw5 u, Sw6 d, and Sw6 uin FIG. 15 function as a first switching section that switches betweenthe series connection and the parallel connection of the capacitiveelements C4 a, C3 a, C2 a, C1 a, and C51 in the first CP circuit 51.

In addition, when the voltages V′, V₂, represent a first voltage, asecond voltage, respectively, the wires 511, 512, . . . , correspond toa first signal path, a second signal path, . . . , respectively.Therefore, in the status A of FIG. 17 or FIG. 18A, one end of thecapacitive element C61 that holds the voltage V₁ becomes a firstconnection point and one end of the capacitive element C62 that holdsthe voltage V₂ becomes a second connection point.

When the statuses A and B are repeated alternately, the voltage Vp/5equalized in the status B is increased one to five times as high by theseries connection of the status A and the voltages are held in thecapacitive elements C51 to C55. Among these hold voltages, one end ofthe capacitive element C53 as the voltage 3Vp/5, one end of thecapacitive element C52 as voltage 2Vp/5, and the voltages Vp and G aresupplied to the switching device 535.

According to the present embodiment, the voltage 4Vp/5 that is one endof capacitive element C54 and the voltage Vp/5 that is one end of thecapacitive element C51 are not used in the configuration.

FIG. 17 is a diagram illustrating an example of a configuration of thesecond CP circuit 52.

As illustrated in FIG. 15, the second CP circuit 52 is configured tohave switches Sw2 d, Sw2 u, Sw3 d, Sw3 u, Sw4 d, Sw4 u, Sw5 d, Sw5 u,Sw6 d, and Sw6 u, and capacitive elements C61, C62, C63, C64, C65, C66,C1 b, C2 b, C3 b, C4 b, and C5 b.

That is, the second CP circuit 52 has a configuration (five-stage pluscapacitive element C61) in which the number of stages is increased byone stage in terms of a circuit compared to the first CP circuit 51.

FIGS. 18A and 18B are diagrams illustrating the connection status of theswitches in the second CP circuit 52.

In the status A, while the capacitive elements C5 b, C4 b, C3 b, C2 b,C1 b, and C61 are connected in series between the output terminals Out-Hand Out-L of the switching device 535, in the status B, the capacitiveelements C5 b, C4 b, C3 b, C2 b, C1 b, and C61 are connected inparallel.

Therefore, the switches Sw2 d, Sw2 u, Sw3 d, Sw3 u, Sw4 d, Sw4 u, Sw5 d,Sw5 u, Sw6 d, and Sw6 u in FIG. 17 function as a second switchingsection that switches between the series connection and the parallelconnection of the capacitive elements C5 b, C4 b, C3 b, C2 b, C1 b, andC61 in the second CP circuit 52.

When the statuses A and B are repeated alternately, the voltageequalized in the status B is increased one to six times by the seriesconnection of the status A and the voltages are held respectively in thecapacitive elements C61 to C66. These hold voltages are supplied to thedrivers as the voltages V₁ to V₆. The voltage of the output terminalOut-L of the switching device 535 itself is supplied to the driver 30 asvoltage V₀.

When the piezoelectric element 40 is charged by the driver 30, the holdvoltage is lowered in some of the capacitive elements C62 to C66 in thesecond CP circuit 52. However, the capacitive element, in which the holdvoltage is lowered, is replenished with a charge from the power supplyby the series connection of the status A, and is redistributed andequalized by the parallel connection of the status B.

Meanwhile, when the piezoelectric element 40 is discharged by the driver30, the hold voltage is increased in some of the capacitive elements C61to C66. However, the charge is discharged by the series connection ofthe status A, and is redistributed and equalized by the parallelconnection of the status B.

Accordingly, the charge discharged from the piezoelectric element 40 iscollected in the second CP circuit 52 and is reused as the charge forcharging the piezoelectric element 40.

The voltage that is supplied to the second CP circuit 52 from theswitching device 535 is switched to either the higher-side voltage set(Vp and 2Vp/5) or the lower-side voltage set (3Vp/5 and G), but in thepresent embodiment, the difference is 3Vp/5 in any case, and thus aconfiguration in which no change occurs regardless of the switching isobtained.

If the difference between the voltage sets which are supplied to thesecond CP circuit 52 from the switching device 535 is switched andchanged in a configuration, the charge moves in the second CP circuit 52by the switching. Since the movement of the charge means an occurrenceof loss in an equalizer circuit element, power is wasted.

According to the present embodiment, when the difference between thevoltage sets which are supplied to the second CP circuit 52 from theswitching device 535 is not changed by the switching in a configuration,the charge does not move in the second CP circuit 52 by the switching.Therefore, it is possible to suppress the waste of the power due to themovement of the charge.

According to the present embodiment, a configuration is formed in which,in order not to cause the difference between the voltage sets that aresupplied to the second CP circuit 52 from the switching device 535 to bechanged by the switching, the power supply voltages (Vp and G) areequally divided and a voltage to be used as the higher-side voltage setand a voltage to be used as the lower-side voltage set are selected fromthe equally divided voltages in the first CP circuit 51.

In general, when the capacity of the capacitive load such as thepiezoelectric element 40 is represented by C and the voltage amplitudeis represented by E, energy P accumulated in the capacitive load isrepresented by P=(C·E²)/2

The piezoelectric element 40 is deformed by the energy P and works, andan amount of work of discharging ink is equal to or less than 1% of theenergy P. Accordingly, the piezoelectric element 40 can be considered asa simple capacity. When the capacity C is charged with a constant power,the same energy as (C·E²)/2 is consumed by the charge circuit. Duringdischarging, the same energy is also consumed by the discharge circuit.

Here, in a case where the control signal COM (Vin) changes in a rangefrom the voltage Vp to the voltage G, a configuration may be assumed, inwhich the piezoelectric element 40 is charged and discharged withoutdividing the voltage (Comparative Example 1). In the Comparative Example1, a loss during the charging corresponds to the sum of areas of hatchedregions a in FIG. 20 and a loss during the discharging corresponds to anarea of a hatched region b in FIG. 20.

In contrast, in a case of a first section by the voltage of the controlsignal COM, the second CP circuit 52 according to the present embodimentdivides the voltage into six from the voltage Vp to the voltage 2Vp/5and supplies the divided voltages as the voltages V₆ to V₀ to the driver30. In a case of a second section, the second CP circuit 52 divides thevoltage into six from the voltage 3Vp/5 to the voltage G and suppliesthe divided voltages as the voltages V₆ to V₀ to the driver 30. In thefirst section and the second section, the voltages from the voltage3Vp/5 to the voltage 2Vp/5 are overlapped.

To be more clear, the power supply voltages (Vp and G) are divided intofive and switched to three fifths of the higher-side and three fifths ofthe lower-side. Since three fifths of the voltage is divided into six inthe second CP circuit 52, the power supply voltages (Vp and G) aredivided into ten as a whole. The driver 30 according to the presentembodiment causes the piezoelectric element 40 to be charged anddischarged by using the voltages obtained by dividing a range from thevoltage Vp to the voltage G into ten.

According to the present embodiment, since the charging and dischargingof the piezoelectric element 40 is performed in a stepwise manner, it ispossible to suppress the loss during the charging and the loss duringthe discharging. To be more specific, since the loss during the chargingaccording to the present embodiment corresponds to the sum of areas ofhatched regions a in FIG. 19 and the loss during the dischargingcorresponds to an area of a hatched region b in FIG. 19, it is possibleto suppress the losses during the charging and discharging compared tothe Comparative Example 1.

Further, according to the present embodiment, since the chargedischarged from the piezoelectric element 40 is collected by the secondCP circuit 52 and reused during the charging, it is possible to greatlysuppress the loss as a whole.

In addition, according to the present embodiment, the voltages V₆ to V₀used when the driver 30 causes the piezoelectric element 40 to becharged and discharged are switched between the first section and thesecond section. Therefore, a range from the voltage Vp to the voltage Gis divided into “ten” more than the number of voltage division of “six”by the second CP circuit 52 and the driver 30 causes the piezoelectricelement 40 to be charged and discharged using the ten-divided voltages.

As Comparative Example 2, a configuration is assumed in which the secondCP circuit 52 divides the power supply voltages (Vp and G) without thefirst CP circuit 51 and the switching device 535. Comparative Example 2has a configuration in which the range from the voltage Vp to thevoltage G is divided into six by the second CP circuit 52 and thensupplied to the driver 30. Therefore, according to Comparative Example2, the driver 30 causes the piezoelectric element 40 to be charged anddischarged by using the voltages obtained by dividing the power supplyvoltages (Vp and G) into six such that the voltage Vout follows thecontrol signal Vin. At this time, the loss during the charging accordingto Comparative Example 2 corresponds to the sum of areas of hatchedregions a in FIG. 21 and the loss during the discharging corresponds tothe sum of areas of hatched regions b in FIG. 21. Here, the number ofvoltage division is less compared to “ten” according to the presentembodiment and the sum of the losses is greater compared to the presentembodiment. In other words, the present embodiment is superior toComparative Example 2 in this point.

According to the present embodiment, the higher-side voltage set (Vp and2Vp/5) and the lower-side voltage set (3Vp/5 and G) are overlapped witheach other in a range of the voltages (3Vp/5 and 2Vp/5). That is, aconfiguration is obtained in which, when switching is performed betweenone of the first section in which the higher-side voltage set isselected or the second section in which the lower-side voltage set isselected, and to the other according to the voltage of the controlsignal COM, it is unavoidable to perform the switching through the rangewhere the voltages are overlapped.

In the driver 30 according to the present embodiment, during theincrease of the voltage (or voltage Vout) of the control signal Vin,when the voltage of the control signal Vin approaches the voltage V₆,the current is unlikely to flow in the transistor 341 in the unitcircuit 34 f (because the voltage between the base-emitter is low).Similarly, during the drop of the voltage Vin, when the voltage of thecontrol signal Vin approaches the voltage V₀, the current is unlikely toflow in the transistor 342 in the unit circuit 34 a.

Therefore, in a case where the overlapping range is not provided, thefollowing inconveniences are assumed. That is, in a case where theoverlapping range is not provided, the higher-side of the lower-sidevoltage set and the lower-side of the higher-side voltage set sharevoltages (boundary voltages). When the control signal Vin over theboundary voltages switches from one of the lower-side voltage set or thehigher-side voltage set to the other, the control signal Vin passesthrough the a state where the current is unlikely to flow in thetransistors 341 and 342. Therefore, the following property of thevoltage Vout to the control signal Vin is degraded.

According to the present embodiment, the overlapping range is providedin advance, the switching is performed such that a voltage range afterthe change is maintained during increasing or dropping of the voltageVin (Vout), and thereby it is possible to avoid degrading the followingproperty of the voltage Vout.

In addition, the voltage Vc is positioned in the overlapping range, andthereby the voltage Vout is caused to follow the voltage Vc regardlessof the voltage of the control signal COM even when the switch 232 is inthe OFF state, which is as described above.

According to the present embodiment, the power supply voltages (Vp andG) are divided into the larger number than the number of the voltagedivision of the first CP circuit 51, and thus the low power consumptionis achieved. The invention is not limited to the embodiment in thevoltage division, and various aspects are considered. Next, the aspectsof the voltage division are examined.

FIG. 22 is a block diagram illustrating a configuration of maincomponents of the printing apparatus 1 according to Application Example(1) when focused on one set of the driver 30 and the piezoelectricelement 40.

In the printing apparatus 1, a configuration is described, in which onlythe first CP circuit 51 of the auxiliary power supply circuit 50 isshared by a plurality of sets of the drivers 30 and the piezoelectricelements 40 and the switching device 535 and the second CP circuit 52are not shared by the plurality of sets of the drivers 30 and thepiezoelectric elements 40, that is, a configuration in which a set ofthe driver 30 and the piezoelectric element 40 corresponds to a set ofthe switching device 535 and the second CP circuit 52. In connectionwith this, it is considered that, as one block including not only themain controller 120 and DAC 160, but also the selection section 230(switch 232), the control signal generator 15 outputs the control signalVin.

In FIG. 22, the first CP circuit 51 performs output with respect to thevoltage 4Vp/5 and the voltage Vp/5 which are not used in the presentembodiment. In addition, the switching device 535 is a two-polefour-throw switch and thus selects any one of a first set of thevoltages (Vp and 3Vp/5), a second set of the voltages (4Vp/5 and 2Vp/5),a third set of the voltages (3Vp/5 and Vp/5), or a fourth set of thevoltages (2Vp/5 and G) by an instruction of the voltage comparator 505.

Each of the voltages from the first set to the fourth set is a voltagecorresponding to two fifths of the power supply voltages (Vp and G).

To be more clear, according to Application Example (1), two fifths ofthe voltages from the first set to the fourth set are overlapped by afifth and switched according to the voltage of the control signal Vin.Since two fifths of the voltages are divided into six by the second CPcircuit 52 similar to the embodiment, the power supply voltages (Vp andG) are divided into 15 as a whole (refer to FIG. 23).

In FIG. 22, when the voltage of the control signal Vin becomes equal toor higher than the voltage 3Vp/5 with respect to the switching device535, the voltage comparator 505 issues an instruction of selecting thefirst set of the voltages (Vp and 3Vp/5). When the voltage of thecontrol signal Vin becomes equal to or higher than the voltage 2Vp/5 andless than the voltage 4Vp/5, the voltage comparator 505 issues aninstruction of selecting the second set of the voltages (4Vp/5 and2Vp/5). When the voltage of the control signal Vin becomes equal to orhigher than the voltage Vp/5 and less than the voltage 3Vp/5, thevoltage comparator 505 issues an instruction of selecting the third setof the voltages (3Vp/5 and Vp/5). When the voltage of the control signalVin becomes less than the voltage 3Vp/5 (equal to or higher than voltageG), the voltage comparator 505 issues an instruction of selecting thefourth set of the voltages (2Vp/5 and G).

The voltage comparator 505 that switches between the connections of thefirst CP circuit 51 with the second CP circuit 52 has the hysteresischaracteristic in voltage determination of the control signal Vin.Specifically, as described above, the threshold value used when thevoltage of the control signal Vin is increased is set to be higher thanthe threshold value used when the voltage of the control signal Vin isdropped.

FIGS. 24A to 25D are diagrams illustrating connections of the first CPcircuit 51 with the second CP circuit 52 according to ApplicationExample (1).

In Application Example (1), in the first section, in the switchingdevice 535, the output terminal Out-H has the voltage Vp and the outputterminal Out-L has the voltage 3Vp/5. Therefore, the first CP circuit 51and the second CP circuit 52 are in the connection status as illustratedin FIG. 24A.

In addition, in the second section, in the switching device 535, theoutput terminal Out-H has the voltage 4Vp/5 and the output terminalOut-L has the voltage 2Vp/5. Therefore, the first CP circuit 51 and thesecond CP circuit 52 are in the connection status as illustrated in FIG.24B.

In the third section, in the switching device 535, the output terminalOut-H has the voltage 3Vp/5 and the output terminal Out-L has thevoltage Vp/5. Therefore, the first CP circuit 51 and the second CPcircuit 52 are in the connection status as illustrated in FIG. 25C.

In the fourth section, in the switching device 535, the output terminalOut-H has the voltage 2Vp/5 and the output terminal Out-L has thevoltage G. Therefore, the first CP circuit 51 and the second CP circuit52 are in the connection status as illustrated in FIG. 25D.

FIG. 23 is a diagram illustrating an operation of the auxiliary powersupply circuit 50 at the voltage of the control signal Vin. Since thedescription is the same as in FIG. 5, the details are not described. Thedriver 30 causes the piezoelectric element 40 to be charged anddischarged by using the voltages obtained by dividing the power supplyvoltages (Vp and G) into 15.

In FIG. 23, a period of time in which the voltages of the first set areselected is set as the first section and a period of time in which thevoltages of the second to fourth sets are selected are set as the secondto fourth sections.

According to Application Example (1), the number of the voltage divisionis increased from “10” to “15”, and thus the low power consumption isachieved.

According to Application Example (1), the switching device and thesecond CP circuit 52 are described as corresponding to one set of thedriver 30 and the piezoelectric element 40. Similar to the embodiment,the switching device and the second CP circuit 52 can also be configuredto correspond to the plurality of sets of the drivers 30 and thepiezoelectric elements 40.

However, the following restrictions are accompanied, that is, since thesame voltage set is supplied to the plurality of drivers 30 in theconfiguration in which the switching device 535 and the second CPcircuit 52 correspond to the plurality of sets of the drivers 30 and thepiezoelectric elements 40, it is not possible to cause the plurality ofpiezoelectric elements 40 to be charged or discharged independently fromeach other. Further, the switching device 535 and the second CP circuit52 can be configured to correspond to the plurality of sets of thedrivers 30 and the piezoelectric elements 40 under a condition that aplurality of drive signals COM is prepared and the same drive signal isused to the drivers 30 that share the second CP circuit 52.

FIG. 26 is a block diagram illustrating a configuration of maincomponents in the printing apparatus 1 according to Application Example(2) when focused on one set of the driver 30 and the piezoelectricelement 40.

The printing apparatus 1 has a configuration in which, similar toApplication Example (1), one set of the switching device 535 and thesecond CP circuit 52 corresponds to one set of the driver 30 and thepiezoelectric element 40 and, as one block including the main controller120, the DAC 160, and the selection section 230 (switch 232), thecontrol signal generator 15 outputs the control signal Vin.

Similar to Application Example (1), the first CP circuit 51 outputs thevoltage 4Vp/5 and the voltage Vp/5 which are not used in the embodiment.

In addition, the switching device 535 is a two-pole five-throw switchand thus selects any one of a first set of the voltages (Vp and 2Vp/5),a second set of the voltages (4Vp/5 and 3Vp/5), a third set of thevoltages (3Vp/5 and 2Vp/5), a fourth set of the voltages (2Vp/5 andVp/5) or a fifth set of the voltages (Vp/5 and G) by an instruction ofthe voltage comparator 505.

Each of the voltages from the first set to the fifth set is a voltagecorresponding to a fifth of the power supply voltages (Vp and G).

The second CP circuit 52 according to Application Example (2) isdifferent from that according to the embodiment and Application Example(1) as follows. That is, the second CP circuit 52 according to theembodiment and Application Example (1) is configured to divide thevoltages of the terminals Out-H and Out-L of the switching device 535into six, and the second CP circuit 52 according to Application Example(2) is configured to cause the voltages of the terminals Out-H and Out-Lto be increased 4/3 times and divide the result into four. In otherwords, the second CP circuit 52 according to Application Example (2) isconfigured to divide the voltages of the terminals Out-H and Out-L intothree and output a voltage of a third step high on the higher-side.

In addition, the number of the unit circuits 34 in the driver 30 isreduced from “6” to “4” in accordance with the change of the second CPcircuit 52. Since the details of the driver 30 in which the stages arereduced to four can be inferred by FIG. 7, the description thereof isomitted.

To be more clear, according to Application Example (2), a fifth of thevoltages from the first set to the fifth set are overlapped by a thirdstep and switched according to the voltage of the control signal Vin. Afifth of the voltages are caused to become 4/3 times as high and aredivided into four. However, since a third of the voltages areoverlapped, the power supply voltages (Vp and G) are divided into 15 asa whole, similar to Application Example (1) (refer to FIG. 27).

In FIG. 26, when the voltage of the control signal Vin becomes equal toor higher than the voltage 4Vp/5 (less than the voltage Vp) with respectto the switching device 535, the voltage comparator 505 issues aninstruction of selecting the first set of the voltages (Vp and 4Vp/5).When the voltage of the control signal Vin becomes equal to or higherthan the voltage 2Vp/5 and less than the voltage 4Vp/5, the voltagecomparator 505 issues an instruction of selecting the second set of thevoltages (4Vp/5 and 3Vp/5). When the voltage of the control signal Vinbecomes equal to or higher than the voltage 3Vp/5 and less than thevoltage 3Vp/5, the voltage comparator 505 issues an instruction ofselecting the third set of the voltages (3Vp/5 and 2Vp/5). When thevoltage of the control signal Vin becomes equal to or higher than thevoltage Vp/5 and less than the voltage 2Vp/5, the voltage comparator 505issues an instruction of selecting the fourth set of the voltages (2Vp/5and Vp/5). When the voltage of the control signal Vin becomes less thanthe voltage Vp/5 (equal to or higher than voltage G), the voltagecomparator 505 issues an instruction of selecting the fifth set of thevoltages (Vp/5 and G).

The voltage comparator 505 that switches between the connections of thefirst CP circuit 51 with the second CP circuit 52 has the hysteresischaracteristic in the voltage determination of the control signal Vin.

Specifically, as described above, the threshold value used when thevoltage of the control signal Vin is increased is set to be greater thanthe threshold value used when the voltage of the control signal Vin isdropped.

FIGS. 28A to 30E are diagrams illustrating connections of the first CPcircuit 51 with the second CP circuit 52 according to ApplicationExample (2).

In Application Example (2), in the first section, in the switchingdevice 535, the output terminal Out-H has the voltage Vp and the outputterminal Out-L has the voltage 4Vp/5. Therefore, the first CP circuit 51and the second CP circuit 52 are in the connection status as illustratedin FIG. 28A.

In addition, in the second section, in the switching device 535, theoutput terminal Out-H has the voltage 4Vp/5 and the output terminalOut-L has the voltage 3Vp/5. Therefore, the first CP circuit 51 and thesecond CP circuit 52 are in the connection status as illustrated in FIG.28B.

In the third section, in the switching device 535, the output terminalOut-H has the voltage 3Vp/5 and the output terminal Out-L has thevoltage 2Vp/5. Therefore, the first CP circuit 51 and the second CPcircuit 52 are in the connection status as illustrated in FIG. 29C.

In the fourth section, in the switching device 535, the output terminalOut-H has the voltage 2Vp/5 and the output terminal Out-L has thevoltage Vp/5. Therefore, the first CP circuit 51 and the second CPcircuit 52 are in the connection status as illustrated in FIG. 29D.

In the fifth section, in the switching device 535, the output terminalOut-H has the voltage Vp/5 and the output terminal Out-L has the voltageG. Therefore, the first CP circuit 51 and the second CP circuit 52 arein the connection status as illustrated in FIG. 30E.

The first CP circuit 51 according to Application Example (2) issubstantially the same as that according to the embodiment orApplication Example (1), but the configuration of the second CP circuit52 is slightly different from the others.

The second CP circuit 52 according to Application Example (2) isdescribed in a confirmatory manner.

FIG. 31 is a diagram illustrating an example of a configuration of thesecond CP circuit 52 that is applied to Application Example (2).

As illustrated in FIG. 31, the second CP circuit 52 is configured tohave switches Sw2 d, Sw2 u, Sw3 d, Sw3 u, Sw4 d, and Sw4 u, andcapacitive elements C41, C42, C43, C44, C1 c, C2 c, C3 c. The second CPcircuit 52 is configured to have a total of three stages of two stagesfor dividing the voltages of terminals Out-H and Out-L into three andholding the divided results and a stage for shifting the voltages ofterminals Out-H and Out-L on the higher-side than the voltage of theterminal Out-H and holding the shifted result.

FIGS. 32A and 32B are diagrams illustrating the connection status of theswitches in the second CP circuit 52.

In the status A, while the capacitive elements C3 c, C2 c, C1 c, and C41are connected in series between the output terminals Out-H and Out-L ofthe switching device 535, in the status B, the capacitive elements C3 c,C2 c, C1 c, and C41 are connected in parallel.

When the statuses A and B are repeated alternately, the voltageequalized in the status B is increased one to four times by the seriesconnection of the status A and the voltages are held respectively in thecapacitive elements C41 to C44. These hold voltages are supplied to thedrivers 30 as the voltages V₁ to V₄.

FIG. 27 is a diagram illustrating an operation of the auxiliary powersupply circuit 50 at the voltage of the control signal Vin. Since thedescription is the same as in FIGS. 5 and 23, the details are notdescribed. The driver causes the piezoelectric element 40 to be chargedand discharged by using the voltages obtained by dividing the powersupply voltages (Vp and G) into 15.

In FIG. 27, a period of time in which the voltages of the first set areselected is set as the first section and a period of time in which thevoltages of the second to fifth sets are selected is set as the secondto fifth sections.

According to Application Example (2), similar to Application Example(1), the number of the voltage division is increased from “10” to “15”,and thus the lower power consumption is achieved compared to theembodiment.

According to Application Example (2), the number of voltage divisionitself is the same as Application Example (1) as “15”, but theoverlapped voltage range is narrowed to a third and thus the number ofthe output voltages of the second CP circuit 52 and the number of unitcircuits 34 in the driver 30 are each decreased to two thirds.

Particularly, since the driver 30 is provided for each nozzle, theconfiguration is simplified and it is possible to lower a cost greatly.

Application Example and Modification Example

The invention is not limited to the above described embodiments, but canbe subjected to various applications and modifications as will bedescribed later. Aspects of the applications and modifications whichwill be described later may be used as one aspect selected randomly or aplurality of the aspects selected randomly may be appropriatelycombined.

Duplicating Operation of Unit Circuit

In the driver 30 described above, in a case where the voltage Voutapproaches the voltage V₆ during the increase of the voltage of thecontrol signal Vin, or in a case where the voltage Vout approaches thevoltage V₀ during the drop of the voltage Vin, the current is unlikelyto flow in the transistors 341 and 342. In addition, in the driver 30,not only in these cases, but also in a case where the voltage Voutapproaches the voltages V₁, V₂, V₀, V₄, and V₅, similarly, the currentis unlikely to flow in the transistors 341 and 342.

Application Example (3) in which the state is improved is described.

FIG. 33 is a diagram illustrating a configuration of the driver 30according to Application Example (3). In the driver 30 illustrated inFIG. 33, the comparators 38 a to 38 e in FIG. 7 are each divided intotwo comparators. That is, in FIG. 33, comparators 38 au, 38 ad, 38 bu,38 bd, 38 cu, 38 cd, 38 du, 38 dd, 38 eu, and 38 ed are included.

Here, the first reference signs a to e immediately after the referencesign 38 of the comparator indicate that a is associated with the voltageV₁ and b to e are associated with the voltages V₂, V₃, V₄, and V₅. Forexample, a pair of comparators 38 ad and 38 au is associated with thevoltage V₁ and, for example, a pair of comparators 38 bd and 38 bu isassociated with the voltage V₂.

Further, a pair of comparators includes one comparator corresponding toa lower-side threshold voltage which is lower than the associatedvoltage by α and one comparator corresponding to a higher-side thresholdvoltage which is higher by α. That is, the second reference signs d andu immediately after the reference sign 38 of the comparator indicatethat d corresponds to the lower-side threshold voltage and u correspondsto the higher-side threshold voltage.

Accordingly, for example, the comparator 38 au indicates that thecomparator corresponds to a higher-side threshold voltage which ishigher than the voltage V₁ by α and the comparator 38 bd indicates thatthe comparator corresponds to a lower-side threshold voltage which islower than the voltage V₂ by α.

When the comparator is described not specifically but generally, thedescription is provided without a reference sign. When, in an input end,the voltage Vout of one end is equal to or higher than the thresholdvoltage of the other end, each comparator outputs an H-level signal andwhen the voltage Vout is less than the threshold voltage of the otherend, each comparator outputs an L-level signal. Specifically, forexample, when the voltage Vout is equal to or higher than the thresholdvoltage (V₁−α), the comparator 38 ad outputs the H-level signal and whenthe voltage Vout is less than the threshold voltage (V₁−α), thecomparator 38 ad outputs the L-level signal. In addition, for example,when the voltage Vout is equal to or higher than the threshold voltage(V₂+α), the comparator 38 bu outputs the H-level signal and when thevoltage Vout is less than the threshold voltage (V₂+α), the comparator38 bu outputs the L-level signal.

When the control signal Vin is equal to or higher than the voltage(V₁−α) and less than (V₁+α), the unit circuits 34 a and 34 bcorresponding to the voltage V₁ are in the enable status. Accordingly,in this case, when the control signal Vin exceeds the voltage Vout, thetransistor 341 of the unit circuit 34 a causes the current to flow toone end of the piezoelectric element 40 through the wire 511 and thetransistor 341 of the unit circuit 34 b causes the current to flow toone end of the piezoelectric element 40 through the wire 512. Inaddition, in this case, when the control signal Vin is less than thevoltage Vout, the transistor 342 of the unit circuit 34 a causes thecurrent to flow to one end of the piezoelectric element 40 through thewire 510 and the transistor 341 of the unit circuit 34 b causes thecurrent to flow to one end of the piezoelectric element 40 through thewire 511.

When the piezoelectric element 40 is charged, the wires that supply thecharge have an overlapping portion by two paths in a part, but, similarto the embodiment, basically switch in the order of the wires 511, 512,513, 514, 515, and 516.

FIGS. 34A and 34B are diagrams illustrating examples of setting ofinput-output characteristics of transistors of which, particularly, thetransistors 341 and 342 of the unit circuits 34 a and 34 b arerepresentative. In FIGS. 34A and 34B, H is a portion in which thecontrol signal Vin that is an input signal of the driver 30 matches thevoltage Vout that is the output.

FIG. 34A illustrates an example of a case of setting a region where thecontrol signal Vin is lower than the voltage (Vout−β) within a region inwhich the transistor 341 is in the ON state and where the control signalVin is higher than the voltage (Vout+β) within a region where thetransistor 342 is in the ON state. In this example, when a differencebetween the voltage of the control signal Vin and the voltage Vout iswithin β by control of the voltage Vout to follow the control signalVin, both of the transistors 341 and 342 are in the OFF state.Therefore, since a state in which a through-current flows between thewires which supply the voltage V₁ to the voltage V₅ is avoided, it isadvantageous in terms of the power consumption.

On the other hand, since a region (dead zone) exists in which thetransistors 341 and 342 are in the OFF state and thus the currentcontrol is not performed, the following property of the voltage Vout tothe control signal Vin is degraded. However, when the voltage runs overthe wires 511 to 515, two transistors are in the ON state. Therefore, anoccurrence of a level difference in the voltage Vout is suppressed.

In FIG. 34A, in a state in which the voltage Vout is equal to or higherthan the threshold voltage (V₁−α) less than (V₁+α), when the controlsignal Vin is lower than the (Vout−β), both of the transistor 341 of theunit circuit 34 a and the transistor 341 of the unit circuit 34 b are inthe ON state, and when the control signal Vin is lower than the(Vout+β), both of the transistor 342 of the unit circuit 34 a and thetransistor 342 of the unit circuit 34 b are in the ON state.

In addition, FIG. 34B illustrates an example of a case of setting aregion where the control signal Vin is lower than the voltage (Vout+β)within a region in which the transistor 341 is in the ON state and wherethe control signal Vin is higher than the voltage (Vout−β) within aregion where the transistor 342 is in the ON state. In this example,when a difference between the voltage of the control signal Vin and thevoltage Vout is within β by control of the voltage Vout to follow thecontrol signal Vin, both of the transistors 341 and 342 are in the ONstate. Therefore, since a situation in which a current flows relying onthe ON state of only one transistor does not occur, the switching of thevoltages is performed smoothly and the occurrence of the leveldifference in the voltage Vout is suppressed. Since a state in which athrough-current flows between the wires cannot be avoided by the ONstate of both of the transistors 341 and 342, it is disadvantageous interms of the power consumption.

In FIG. 34B, in a state in which the voltage Vout is equal to or higherthan the threshold voltage (V₁−α) less than (V₁+α), and in a state inwhich a difference between the voltage of the control signal Vin and thevoltage Vout is within β, a total of four of the transistors 341 and 342of the unit circuit 34 a and the transistors 341 and 342 of the unitcircuit 34 b are in the ON state.

It is preferable that the selection of one of the sets in FIGS. 34A and34B be performed by taking into account the power consumption, thefollowing property of the voltage Vout, the smooth switching, and thelike, comprehensively.

Operation Target

According to the embodiment, an example of the piezoelectric element 40that discharges ink is described as a drive target of the driver 30.According to the invention, the drive target is not limited to thepiezoelectric element 40, but, for example, may be any load which has acapacitive component such as an ultrasonic motor, a touch panel, anelectrostatic loudspeaker, or an liquid crystal panel.

The Number of Stages of Unit Circuit or the Like

The embodiment has a configuration in which the six stages of the unitcircuits 34 a to 34 f are provided in ascending order of the voltages tocorrespond to the adjacent two voltages to each other out of the sixtypes of voltages. However, according to the invention, the number ofthe unit circuits 34 is not limited thereto as described in ApplicationExample (2), but may be two or more. The greater the number of the unitcircuits 34, the less the loss during the charging and discharging, butthe more complex the configuration.

In addition, the transistors 341 and 342 in the unit circuit 34 are notlimited to the bipolar type, but may be metal-oxide-semiconductorfield-effect transistors (MOSFET), respectively.

What is claimed is:
 1. A liquid discharge apparatus comprising: a piezoelectric element that is displaced according to a voltage of a drive signal; a cavity which is filled with a liquid and of which an inside volume is expanded and contracted due to the displacement of the piezoelectric element; a nozzle that communicates with the cavity and is capable of discharging the liquid by the expansion and contraction of the inside volume of the cavity; a charge source that supplies a charge to the piezoelectric element; a first signal path to which a first voltage is applied by the charge source; a second signal path to which a second voltage that is higher than the first voltage is applied by the charge source; and a connection path selecting section that causes the piezoelectric element and the charge source to be electrically connected to each other by using the first signal path or the second signal path according to the voltage of a control signal that controls the voltage of the drive signal and a hold voltage of the piezoelectric element, wherein the charge source includes: a first auxiliary power source that outputs two types or more of voltages; and a second auxiliary power source that outputs three types or more of voltages which is used to be applied to the piezoelectric element by using the two types or more of voltages output from the first auxiliary power source.
 2. The liquid discharge apparatus according to claim 1, wherein the first auxiliary power source includes: m (m is a plural number) capacitive elements; and a first switching section that switches between a series status in which the m capacitive elements are electrically connected in series and a parallel status in which the m capacitive elements are electrically connected in parallel, and wherein the second auxiliary power source includes: n (n is a plural number) capacitive elements; and a second switching section that switches between a series status in which the n capacitive elements are electrically connected in series and a parallel status in which the n capacitive elements are electrically connected in parallel.
 3. The liquid discharge apparatus according to claim 2, wherein, in the second auxiliary power source, in the series status, any first point of connection points of the n capacitive elements to one another is connected to the first signal path and a second point on the higher side than the first point of the connection points of the n capacitive elements to one another is connected to the second signal path.
 4. The liquid discharge apparatus according to claim 2, wherein the first auxiliary power source supplies, to the second auxiliary power source, at least one of a higher-side voltage set in which the higher side becomes an A voltage and a lower-side voltage set in which the higher side becomes a B voltage that is lower than the A voltage.
 5. The liquid discharge apparatus according to claim 4, wherein the first auxiliary power source supplies, to the second auxiliary power source, the higher-side voltage set in a case where the voltage of the drive signal is a first drive voltage and the lower-side voltage set in a case where the voltage of the drive signal is a second drive voltage which is lower than the first drive voltage.
 6. The liquid discharge apparatus according to claim 5, wherein a third drive voltage which is lower than the first drive voltage and higher than the second drive voltage is included both in a voltage range of the higher-side voltage set and in a voltage range of the lower-side voltage set.
 7. A head unit comprising: a piezoelectric element that is displaced according to a voltage of a drive signal; a cavity which is filled with a liquid and of which an inside volume is expanded and contracted due to the displacement of the piezoelectric element; a nozzle that communicates with the cavity and is capable of discharging the liquid by the expansion and contraction of the inside volume of the cavity; a charge source that supplies a charge to the piezoelectric element; a first signal path to which a first voltage is applied by the charge source; a second signal path to which a second voltage that is higher than the first voltage is applied by the charge source; and a connection path selecting section that causes the piezoelectric element and the charge source to be electrically connected to each other by using the first signal path or the second signal path according to the voltage of a control signal that controls the voltage of the drive signal and a hold voltage of the piezoelectric element, wherein the charge source includes: a first auxiliary power source that outputs two types or more of voltages; and a second auxiliary power source that outputs three types or more of voltages in order to apply to the piezoelectric element by using the two types or more of voltages output from the first auxiliary power source.
 8. A control method of a liquid discharge apparatus that includes: a piezoelectric element that is displaced according to a voltage of a drive signal; a cavity which is filled with a liquid and of which an inside volume is expanded and contracted due to the displacement of the piezoelectric element; a nozzle that communicates with the cavity and is capable of discharging the liquid by the expansion and contraction of the inside volume of the cavity; a charge source that supplies a charge to the piezoelectric element; a first signal path to which a first voltage is applied by the charge source; and a second signal path to which a second voltage that is higher than the first voltage is applied by the charge source, wherein the charge source includes: a first auxiliary power source that outputs two types or more of voltages; and a second auxiliary power source that outputs three types or more of voltages in order to apply to the piezoelectric element by using the two types or more of voltages output from the first auxiliary power source, the method comprising: causing the piezoelectric element and the charge source to be electrically connected to each other by using the first signal path or the second signal path according to the voltage of a control signal that controls the voltage of the drive signal and a hold voltage of the piezoelectric element. 